1. Field of the Invention
This invention relates to a finishing sander having a flat rectangular sanding plate to which a sheet of sandpaper is clamped for effecting a smooth finish on a plane workpiece surface. More particularly, this invention relates to a cordless or battery-operated finishing sander having a clamping arrangement by means of which the sandpaper can be easily replaced.
2. Description of the Prior Art
The prior art finishing sanders include a power cord for the drive motor as disclosed in U.S. Pat. Nos. 3,345,784, 3,418,761 and 4,242,839 for example. It has been found that by the power cord arrangement, the finishing sanders have a limited range of movement, thereby reducing their maneuverability. Moreover, in these finishing sanders, a balance of weight is not obtained among the handle portion including the electric switch and the power cord, the motor housing and the skirt portion, particularly with respect to the longitudinal direction about the axis of the motor drive shaft. In order to cope with such problems, a second or forward control handle or the like is provided to maintain good weight balance of the sander.
In most of such constructions of sanders, a paper clamping arrangement is provided on the sanding plate. For example, U.S. Pat. Nos. 3,336,702 and 3,418,761 disclose a paper clamp member having knurled cylindrical sections by means of which the sandpaper is detachably gripped. With this construction, however, a screw driver or the like tool is required to turn the clamp member and thus considerable force is required to clamp the sandpaper to the sanding plate.
U.S. Pat. Nos. 3,345,784 and 2,914,889 disclose a clamp mechanism wherein the sandpaper is resiliently gripped on the sanding plate by a torsion spring. In clamping a sheet of sandpaper, the operator moves a clamp member depressed by the spring away from the sanding plate and, while holding this position by his one hand, he inserts the sandpaper with his other hand. It is recognized that exchange of sandpaper is inconvenient and considerable effort is required.
Various clamping mechanisms have been devised heretofore to facilitate the replacement of sandpaper. For example, U.S. Pat. No. 4,075,793 discloses a power sander including a clamping mechanism wherein the clamping member can be retained in the open position for more efficient replacement of the sandpaper. In this sander, however, a part of the clamping mechanism projects from the upper side of the skirt. During the operation, therefore, the sander may often engage a solid object or the operator's hand thereby actuating the clamping mechanism to unclamp the sandpaper. The projection may come into contact with the operator's body thereby resulting in injury. Further, the clamping mechanisms are provided on the opposite sides of the skirt. Apparently, this adds to the size of the sanding plate and ultimately of the sander body. Thus, this type of sander is unsuitable for a cordless or battery-operated sander.